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1.
The effect of varied Zn supply on the pH of the nutrient solution and uptake of cations and anions was studied in cotton (Gossypium hirsutum L.), sunflower (Helianthus annuus L.) and buckwheat (Fagopyrum esculentum Moench) plants grown under controlled environmental conditions in nutrient solutions with nitrate as source of nitrogen. With the appearance of visual Zn deficiency symtoms, the pH of the nutrient solutions decreased from 6 to about 5 whereas the pH increased to about 7 when the plants were adequately supplied with Zn. In Zn deficient plants the pH decrease was associated with a shift in the cation-anion uptake ratio in favour of cation uptake. Of the major ions, uptake of Ca2+ and K+ was either not affected or only slightly lowered whereas NO3 - uptake was drastically decreased in Zn deficient plants. Although the Zn nutritional status of plants hardly affected the NO3 - concentrations in the plants, the leakage of NO3 - from roots of Zn deficient plants into a diluted CaCl2 solution was nearly 10 times higher than that of plants adequately supplied with Zn. In contrast to Zn deficiency, Mn deficiency in cotton plants neither affected NO3 - uptake nor the pH of the nutrient solution.The results indicate that, probably as a consequence of the role of Zn in plasma membrane integrity and nitrogen metabolism, when Zn is deficient in dicotyledonous species net uptake of NO3 - is particularly depressed which in turn results in an increase in cation-anion uptake ratio and a corresponding decrease in external pH. The ecological relevance of this rhizosphere acidification is discussed.  相似文献   

2.
Kovács K  Kuzmann E  Tatár E  Vértes A  Fodor F 《Planta》2009,229(2):271-278
Distinct chemical species of iron were investigated by Mössbauer spectroscopy during iron uptake into cucumber roots grown in unbuffered nutrient solution with or without 57Fe-citrate. Mössbauer spectra of iron deficient roots supplied with 10–500 μM 57Fe-citrate for 30–180 min and 24 h and iron-sufficient ones, were recorded. The roots were analysed for Fe concentration and Fe reductase activity. The Mössbauer parameters in the case of iron-sufficient roots revealed high-spin iron(III) components suggesting the presence of FeIII-carboxylate complexes, hydrous ferric oxides and sulfate–hydroxide containing species. No FeII was detected in these roots. However, iron-deficient roots supplied with 0.5 mM 57FeIII-citrate for 30 min contained significant amount of FeII in a hexaaqua complex form. This is a direct evidence for the Strategy I iron uptake mechanism. Correlation was found between the decrease in Fe reductase activity and the ratio of FeII–FeIII components as the time of iron supply was increased. The data may refer to a higher iron reduction rate as compared to its uptake/reoxidation in the cytoplasm in accordance with the increased reduction rate in iron deficient Strategy I plants.  相似文献   

3.
The uptake of the radioactive ammoniumanalogue 14C-methylammonium1 was measured in heterotrophically grown cells of Alcaligenes eutrophus H16 in order to study the mechanism of NH 4 + uptake. MA gradients of up to 200 were built up by a substrate-specific and energy-dependent system which showed a K m of 35–111 M and a V max of 0.4–1.8 nmol MA/min per mg protein. The involved carrier exhibited a higher affinity towards NH 4 + than towards CH3NH 3 + indicating that ammonium rather than MA was its natural substrate. Cold shock with hypotonic but not with hypertonic solutions caused the efflux of almost the entire accumulated MA. Osmotic shock did not affect the uptake reaction, suggesting that no periplasmic binding proteins were involved. Indirect observations indicate the membrane potential as driving force for MA uptake. High rates of uptake were observed in cells grown under nitrogen deficiency or with nitrate as nitrogen source. The uptake rate decreased during growth at high ammonium concentrations indicating that biosynthesis of nitrogenous compounds was supported by passive diffusion of NH3. The data suggest that the formation of the carrier is subject to nitrogen control.Non-standard abbreviations CCCP Carbonylcyanide-m-chlorphe-nylhydazone - MA methylammonium - pCMB para-chlormercuribenzoate  相似文献   

4.
Iron transport in Escherichia coli K-12   总被引:14,自引:0,他引:14  
The study of iron uptake promoted by 2,3-dihydroxybenzoate (DHB) into Escherichia coli K-12 aroB mutants allowed some dissection of outer and cytoplasmic membrane functions. These strains are unable to produce the iron-transporting chelate enterochelin, unless fed with a precursor such as DHB. When added to the medium, enterochelin and its natural breakdown products, the linear dimer and trimer of 2,3-dihydroxybenzoylserine (DBS), efficiently transported iron via the feuB, tonB and fep gene products. Thus mutants in these genes were defective in transport of the above chelates. However, feuB and tonB mutants were able to take up iron when DHB was added to the medium. Thus DHB-promoted iron uptake bypassed two functions required for the transport of ferric-enterochelin from the medium. One of these functions, feuB, has been shown to be an outer membrane protein. In contrast to three other iron transport systems including ferric-enterochelin uptake, DHB-promoted iron uptake was little affected by the uncoupler 2,4-dinitrophenol. Dissipation of the energized state of the cytoplasmic membrane apparently only affects those iron transport systems which require an outer membrane protein. Since DHB-promoted iron uptake bypasses the feuB outer membrane protein and the tonB function, it is concluded that, in ferricenterochelin transport, the tonB gene may function in coupling the energized state of the cytoplasmic membrane to the protein-dependent outer membrane permeability. DHB-promoted iron uptake required the synthesis and enzymatic breakdown of enterochelin as judged by the effects of the entF and fesB mutations. A fep mutant was not only deficient in the transport of the ferric chelates of enterochelin and its breakdown products, but was also deficient in DHB-promoted iron uptake. A scheme is presented in which iron diffuses as DHB-complex through the outer membrane, and is subsequently captured by enterochelin or DBS dimer or trimer and translocated across the cytoplasmic membrane.List of Abbreviations DHB 2,3-dihydroxybenzoate - DBS 2,3-dihydroxybenzoylserine - NTA nitrilotriacetate - DNP 2,4-dinitrophenol  相似文献   

5.
Summary Absorption of nitrate and ammonium was studied in water culture experiments with 4 to 6 weeks old plants of barley (Hordeum vulgare L.), buckwheat (Fagopyrum esculentum L. Moench) and rape (Brassica napus L.). The plants were grown in a complete nutrient solution with nitrate (5.7±0.2 mM) or nitrate (5.6±0.2 mM) + ammonium (0.04±0.02 mM). The pH of the nutrient solution was kept at 5.0 using a pH-stat. It was found that phosphorus deficiency reduced the rate of nitrate uptake by 58±3% when nitrate was the sole N source and by 83±1% when both nitrate and ammonium were present. The reduction occurred even before growth was significantly impeded by P deficiency. The inhibition of the uptake of ammonium was less,i.e. ammonium constituted 10±1% of the total N uptake in the P sufficient plants and 30±5% in the P deficient plants. The reduction of nitrate absorption greatly decreased the difference between the uptake of anions and cations. It is suggested that P deficiency reduced the assimilation of NO 3 into the proteins, which might cause a negative feedback on NO 3 influx and/or stimulate NO 3 efflux.  相似文献   

6.
Absorption from food is an important route for entry of the toxic metal, cadmium, into the body. Both cadmium and iron are believed to be taken up by duodenal enterocytes via the iron regulated, proton-coupled transporter, DMT1. This means that cadmium uptake could be enhanced in conditions where iron absorption is increased. We measured pH dependent uptake of 109Cd and 59Fe by duodenum from mice with an in vitro method. Mice with experimental (hypoxia, iron deficiency) or hereditary (hypotransferrinaemia) increased iron absorption were studied. All three groups of mice showed increased 59Fe uptake (p<0.05) compared to their respective controls. Hypotransferrinaemic and iron deficient mice exhibited an increase in 109Cd uptake (p<0.05). Cadmium uptake was not, however, increased by lowering the medium pH from 7.4 to 6. In contrast, 59Fe uptake (from 59FeNTA2) and ferric reductase activity was increased by lowering medium pH in control and iron deficient mice (p<0.05). The data show that duodenal cadmium uptake can be increased by hereditary iron overload conditions. The uptake is not, however, altered by lowering medium pH suggesting that DMT1-independent uptake pathways may operate.  相似文献   

7.
Long-distance signals generated in shoots are thought to be associated with the regulation of iron uptake from roots; however, the signaling mechanism is still unknown. To elucidate whether the signal regulates iron uptake genes in roots positively or negatively, we analyzed the expressions of two representative iron uptake genes: NtIRT1 and NtFRO1 in tobacco (Nicotiana tabacum L.) roots, after shoots were manipulated in vitro. When iron-deficient leaves were treated with Fe(II)-EDTA, the expressions of both genes were significantly reduced; nevertheless iron concentration in the roots maintained a similar level to that in roots grown under iron-deficient conditions. Next, all leaves from tobacco plants grown under the iron-deficient condition were excised. The expression of two genes were quickly reduced below half within 2 h after the leaf excision and gradually disappeared by the end of a 24-h period. The NtIRT1 expression was compared among the plants whose leaves were cut off in various patterns. The expression increased in proportion to the dry weight of iron-deficient leaves, although no relation was observed between the gene expression and the position of excised leaves. Interestingly, the NtIRT1 expression in hairy roots increased under the iron-deficient condition, suggesting that roots also have the signaling mechanism of iron status as well as shoots. Taken together, these results indicate that the long-distance signal generated in iron-deficient tissues including roots is a major factor in positive regulation of the expression of NtIRT1 and NtFRO1 in roots, and that the strength of the signal depends on the size of plants.  相似文献   

8.
Iron(II) exacerbates the effects of oxidative stress via the Fenton reaction. A number of human diseases are associated with iron accumulation including ischemia-reperfusion injury, inflammation and certain neurodegenerative diseases. The functional properties and localization in plasma membrane of cells and endosomes suggest an important role for the divalent metal transporter DMT1 (also known as DCT1 and Nramp2) in iron transport and cellular iron homeostasis. Although iron metabolism is strictly controlled and the activity of DMT1 is central in controlling iron homeostasis, no regulatory mechanisms for DMT1 have been so far identified. Our studies show that the activity of DMT1 is modulated by compounds that affect its redox status. We also show that both iron and zinc are transported by DMT1 when expressed in Xenopus laevis oocytes. Radiotracer uptake and electrophysiological measurements revealed that H2O2 and Hg2+ treatments result in substantial inhibition of DMT1. These findings may have a profound relevance from a physiological and pathophysiological standpoint. Present address for D.T.: Department of Neurology, Cecil B. Day Laboratory for Neuromuscular Research, Massachusetts General Hospital, Harvard Medical School, Charlestown, MA 02129, USA  相似文献   

9.
Protoplasts ofBifidobacterium thermophilum were prepared by a combination of lysozyme and protease digestion, and ferrous iron uptake studies were carried out. Little, if any, iron was internalized by the protoplasts, although large amounts of iron were bound to the protoplast surface. This binding was much greater than that of intact cells, which prefer to internalize iron by an energy-dependent process. It was also found that the binding of iron by protoplasts of cells grown in an iron-deficient medium was much more extensive than that of cells grown in an iron-sufficient medium. Soluble and particulate fractions of protoplasts were prepared by grinding them in a glass homogenizer, and the particulate fraction was also subjected to iron binding studies. The amount of iron bound was the same as that in intact protoplasts, indicating that the particulate fraction membrane fragments bound iron on their outer surface only. Nevertheless, when iron-preloaded cells were protoplasted and their surface cleared of iron, their particulate fraction contained considerable amounts of iron, indicating that the inner surface of the membranes is capable of binding iron as long as the cell is intact. The amount of iron so bound was dose-dependent on the amount of iron entering the cell. The failure of the outer and inner surface iron pools to mix was confirmed by the fact that when iron-preloaded protoplasts were incubated with additional iron, only the latter (surface-bound) was elutable with nonradioactive 2 mM FeSO4. It is concluded that increasing bifidobacterial iron load increases the amount of iron bound to the inner surface of the membrane; the procedure, which is effective in forming bifidobacterial protoplasts, destroys their iron transport mechanism while uncovering surface iron-binding sites; and that such iron-binding sites may be of significance in the cellular iron metabolism processes.  相似文献   

10.
Pseudomonas aeruginosa samples were studied using Mössbauer spectroscopy and electron paramagnetic resonance (EPR). Samples included whole cells, membranes, and soluble fractions from cells which had been grown with57ferric chloride,57ferric citrate or incubated with57ferripyoverdine. These experiments show for the first time thatP. aeruginosa can accumulate iron in a bacterioferritin when grown under conditions of iron limitation and incubated with its cognate ferrisiderophore, ferripyoverdine. Soluble fraction fromP. aeruginosa cells which were grown iron starved and incubated with57ferripyoverdine for 120 min showed the presence of both a ferric and ferrous complex whose Mössbauer spectra matched that of bacterioferritin extracted fromAzotobacter vinelandii and whose EPR spectra showed a characteristic ferritin-like resonance. A second soluble fraction sample from cells which had been grown with57ferric citrate also showed the presence of a species with the same EPR and Mössbauer parameters. In addition Western blotting confirmed the presence of bacterioferritin in the soluble fraction of the cells which had been incubated with ferripyoverdine.  相似文献   

11.
Iron-uptake is well studied in a plethora of pro- and eukaryotic organisms with the exception of Archaea, which thrive mainly in extreme environments. In this study, the mechanism of iron transport in the extremely halophilic Euryarchaeon Halobacterium salinarum strain JW 5 was analyzed. Under low-iron growth conditions no siderophores were detectable in culture supernatants. However, various xenosiderophores support growth of H. salinarum. In [55Fe]–[14C] double-label experiments, H. salinarum displays uptake of iron but not of the chelator citrate. Uptake of iron was inhibited by cyanide and at higher concentrations by Ga. Furthermore, a KM for iron uptake in cells of 2.36 μM and a Vmax of approximately 67 pmol Fe/min/mg protein was determined. [55Fe]-uptake kinetics were measured in the absence and presence of Ga. Uptake of iron was inhibited merely at very high Ga concentrations. The results indicate an energy dependent iron uptake process in H. salinarum and suggest reduction of the metal at the membrane level.  相似文献   

12.
Summary The effects of aluminium (Al3+) at concentrations of 0, 25, 50 and 100 μM on the growth of white clover, dependent upon N supplied as NO 3 , were examined in flowing solution culture. Plants were established with a normal nutrient supply for 7 weeks and then grown with carefully controlled pH (at 4.5) and P concentrations, and with 0, 25, 50 or 100 μM Al3+ for a further three weeks. There were rapid visual effects (i.e. symptoms of P deficiency and reduction in root extension) and the dry weights of shoots and roots were reduced at 50 and 100 μM. Less than 10% of Al absorbed from solution was transported to the shoots. The uptake of P, and its transport between roots and shoots, were reduced in plants grown with Al. The uptake of NO 3 stopped immediately after the introduction of 50 or 100 μM Al, and was significantly reduced at 25 μM after three weeks. During a second phase of the experiment, plants previously grown at 0, 25, 50 and 100 μM Al, were grown for a further 2 weeks either with NO 3 (with and without 50 μM Al3+) or without NO 3 but with inoculation by Rhizobia (and with or without 50 μM Al3+). The effects of the previous treatments with Al on N uptake were small during the second phase, but uptake by all plants was restricted when Al was present. Inoculation did not result in nodulation in the second phase when Al3+ was present in the solution, but Al already in the plant from the first phase did not prevent nodulation in the absence of Al during the second phase.  相似文献   

13.
Observations of near-bottom populations of Karenia brevis suggest that these cells may derive nutrients from the sediment–water interface. Cells undergoing a metabolic-mediated migration may be in close proximity to enhanced concentrations of nutrients associated with the sediment during at least a fraction of their diel cycle. In this study, the growth, uptake and assimilation rates of ammonium, nitrate, and urea by K. brevis were examined on a diel basis to better understand the potential role of these nutrients in the near-bottom ecology of this species. Three strains of K. brevis, C6, C3, and CCMP 2229, were grown under 12:12 light dark cycle under 30 μmol photons m−2 s−1 delivered to the surface plain of batch cultures. Nitrogen uptake was evaluated using 15N tracer techniques and trichloroacetic acid extraction was used to evaluate the quantity of nitrogen (N) assimilated into cell protein. Growth rates ranged from a low of 0.12 divisions day−1 for C6 and C3 grown on nitrate to a high of 0.18 divisions day−1 for C3 grown on urea. Diurnal maximum uptake rates, ρmax, varied from 0.41 pmol-N cell−1 h−1 for CCMP 2229 grown on nitrate, to 1.29 pmol-N cell−1 h−1 for CCMP 2229 grown on urea. Average nocturnal uptake rates were 29% of diurnal rates for nitrate, 103% of diurnal uptake rates for ammonium and 56% of diurnal uptake rates for urea. Uptake kinetic parameters varied between substrates, between strains and between day and night measurements. Highest maximum uptake rates were found for urea for strains CCMP2229 and C3 and for ammonium for strain C6. Rates of asmilation into protein also varied day and night, but overall were highest for urea. The comparison of maximal uptake rates as well as assimilation efficiencies indicate that ammonium and urea are utilized (taken up and assimilated) more than twice was fast as nitrate on a diel basis.  相似文献   

14.
R. W. Ruess 《Oecologia》1988,77(4):550-556
Summary Sporobolus kentrophyllus, a grazing-tolerant C4 grass from the southeastern Serengeti Plains, was grown in solution culture to examine the effects of clipping on the uptake, preference and subsequent transport of varying nitrogen forms. Clipping reduced offtake mass, crown mass ane root mass, resulting in a 58% decline in plant mass. Proportional biomass allocation to roots decreased with clipping, while tillering rates increased. Clipping also increased the nitrogen concentrations of all tissues, and plant nitrogen uptake (nitrogen accumulated throughout the experiment per gram root). The 15N concentrations (% atom excess) of all tissues were higher in clipped compared with unclipped plants, and the average 15N uptake rate of clipped plants was twice that of unclipped plants. The relative 15N allocation to aboveground mass, a measure of canopy sink strength, was higher in clipped plants. Plants fed 15N-ammonium or 15N-nitrate during the 15N pulse experiment had greater 15N tissue concentrations compared with urea-fed plants, and 15N uptake rates were higher in ammonium-fed and nitrate-fed plants, compared with urea-fed plants. The relative magnitudes of these differences were higher when plants were clipped. Clipped plants had higher uptake rates for potassium, phosphorus and sodium, while differences between clipping treatments for calcium, iron, and magnesium were indistinguishable. Rapid uptake rates for species on the southeastern Serengeti plains, particularly during grazing periods, have important implications for nutrient cycling in this system.  相似文献   

15.
Nitrogen, phosphorus and potassium deficiency reduced the uptake of32P-phosphate,35S-sulphate,24Na-,42K-,45Ca-,54Mn-,59Fe- and65Zn- byCicer arietinum (Bengal gram) cv B-75. Root length, leaf area and dry weight of the tissues were also reduced. Since in several cases, the total contents of the radio nucleides both on per plant and per unit dry weight basis were curtailed, the decrease in uptake of several ions cannot be entirely due to reduced growth rate. The reduction in32P-phosphate uptake was more severe with nitrogen deficient plants than that in phosphate deficient ones; potassium deficient plants, however, took up42K- as avidly as the control plants. Simultaneously the uptake of35SO4 2- and other cations was affected particularly by nitrogen deficiency. The distribution of radionucleides between the root and shoot portions was also disturbed in several cases by deficiency conditions. The radionucleides taken up accumulated in the young regions as in the case of pea and other dicotyledonous plants. Mobilization of32P and35S in the reproductive plants was most markedly affected by nitrogen and potassium-deficiency.  相似文献   

16.
The photoreactivep-azidobenzoyl analog of ferrioxamine B was used to show that ferrioxamine-B-mediated iron transport is separate and distinct from coprogen-mediated iron transport inEscherichia coli. Photolysis of this analog inhibited uptake of [59Fe]ferrioxamine B but not [59Fe]coprogen or [59Fe]ferrichrome. Conversely, photolysis of thep-azidobenzoyl analog of coprogen B inhibited uptake of [59Fe]coprogen but not [59Fe]ferrioxamine B or [59Fe]ferrichrome. Photolabeling of outer membranes withp-azidobenzoyl-[59Fe]ferrioxamine B resulted in the labeling of two iron-regulated peptides with molecular masses of about 66 and 26 kDa. Expression of these peptides was increased when ferrioxamine B was the sole iron source. Both peptides were present in outer membrane preparations of thefhuF mutant H1717, but the 66 kDa peptide was not inducible. These results are evidence for an outer membrane receptor inE. coli unique for linear ferrioxamines.  相似文献   

17.
Resting cells of Clostridium sticklandii took up thymine or uracil, when grown in a medium containing 40 mM serine and 20 mM thymine or uracil. The uptake was much lower, when the cells had been grown in a complex medium. Cell-free extracts from cells grown in the complex medium reduced the two bases to the dihydro compounds and decomposed dihydrothymine to -ureidoisobutyrate, as indicated by thin-layer chromatography. Uptake and degradation were stimulated by both NADH and NADPH. Further breakdown did not occur, as 14CO2 was not evolved from C-2-labelled thymine or uracil. The rates of pyrimidine uptake and breakdown of C. sticklandii were lower than those reported for C. sporogenes (Hilton et al., 1975).  相似文献   

18.
Differentially labelled 35S-thiosulphate was taken up by washed cells of Thiobacillus ferrooxidans which were previously grown on thiosulphate. The uptake was proportional to the biomass over the range 0.5–4.0 mg dry wt. of bacteria and showed typical saturation kinetics with an estimated K m value of 0.5 mM for 35S-thiosulphate. Dithionate and Group VI anions inhibited the uptake, which was under pH control and had a temperature optimum of 50°C. In the absence of thiosulphate, the cells bound 35S-sulphate but the binding did not increase on prolonged incubation and the label could be removed completely by washing with dilute sulphuric acid. Increasing amounts of the label were incorporated from [outer-35S]thiosulphate into cellular materials over a 60-min period, whereas little or no assimilation was observed from either the [inner-35S]thiosulphate or 35S-sulphate. The kinetic properties of the sulphate-activating enzyme ATP_sulphurylase enriched from bacteria grown with either thiosulphate or ferrous-iron were similar although this enzyme has an assimilatory function only when the bacterium is grown with ferrous-iron.Abbreviation APS adenosine-5-sulphatophosphate  相似文献   

19.
Henia Mor  Isaac Barash 《Biometals》1990,2(4):209-213
Summary Geotrichum candidum is capable of utilizing iron from hydroxamate siderophores of different structural classes. The relative rates of iron transport for ferrichrome, ferrichrysin, ferrioxamine B, fusigen, ferrichrome A, rhodotorulic acid, coprogen B, dimerium acid and ferrirhodin were 100%, 98%, 74%, 59%, 49%, 35%, 24%, 12% and 11% respectively. Ferrichrome, ferrichrysine and ferrichrome A inhibited [59Fe]ferrioxamine-B-mediated iron transport by 71%, 68% and 28% respectively when added at equimolar concentrations to the radioactive complex. The inhibitory mechanism of [59Fe]ferrioxamine B uptake by ferrichrome was non-competitive (K i 2.4 M), suggesting that the two siderophores do not share a common transport system. Uptake of [59Fe]ferrichrome, [59Fe]rhodotorulic acid and [59Fe]fusigen was unaffected by competition with the other two siderophores or with ferrioxamine B. Thus,G. candidum may possess independent transport systems for siderophores of different structural classes. The uptake rates of [14C]ferrioxamine B and67Ga-desferrioxamine B were 30% and 60% respectively, as compared to [59Fe]ferrioxamine B. The specific ferrous chelates, dipyridyl and ferrozine at 6 mM, caused 65% and 35% inhibition of [59Fe]ferrioxamine uptake. From these results we conclude that, although about 70% of the iron is apparently removed from the complex by reduction prior to being transported across the cellular membrane, a significant portion of the chelated ligand may enter the cell intact. The former and latter mechanisms seem not to be mutually exclusive.  相似文献   

20.
Chlorophyll (Chl), phycoerythrin (PE), total nitrogen (TN% dw) and Fein tissues were measured in Fe-deficient cultures of Gracilariatenuistipitata var. liui over a period of 60 days. 55Fe uptakeand photosynthetic carbon fixation (NaH14CO3) werecompared in Fe-rich and Fe-deficient cultures and analyzed the effects ofFe-deficiency on the ultrastructure. The maximum carbon fixationdecreased significantly (p < 0.01) under Fe-deficiency. Thechlorophyll and phycoerythrin contents also declined with decreasing tissueiron content, falling, respectively, to 7.9 and 33.8% of their originallevel. Photosynthesis in Fe-deficient cells became light-saturated at lowerirradiance than the control. Total N in tissue decreased from 3.65 to2.49%. 55Fe uptake rate for cultures grown on NO3 -was measured following resuspension in either NH4 + orNO3 - as N source. Enhanced Fe uptake developedunder Fe stress, especially with cells resuspended in NH+ 4-N medium. The Vmaxfor Fe uptake was higher with NH4 + thanNO3 - (62.8 versus 12.1 pmol mg dw-1 h-1). The requirement for N accelerates further Fe uptake. Ultrastructuralobservations of Fe-deficient cells showed reductions in chloroplast number,degeneration of lamellar organization, decrease in mitochondrial matrixdensity and variation in accumulation body number and morphology. During Fe-deficiency, the growth rate continued to decline and after 40days of iron deficiency, no further growth was detectable, and eventuallyiron deficiency resulted in chlorosis. The results suggest that the lowergrowth rate of Gracilaria tenuistipitata var. liui underFe-deficiency may result from largely from inhibition of photosynthesis andnitrogen utilization.  相似文献   

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